1. Field of the Invention
The present invention relates to a method of manufacturing an illumination device, an illumination device, an illumination device manufacturing system, and a method of classifying color tone of light emitting devices.
2. Description of the Related Art
In recent years, light emitting chips (semiconductor light emitting elements) as well as light emitting devices, which combine a light emitting element with phosphor material that absorbs light from the light emitting element and re-emits light at a different wavelength from the light emitting element, have been used in various types of illumination (lighting) devices. However, even when the light emitting devices are manufactured in the same manner, semiconductor chip and phosphor variation results in light emitting devices with different color temperature, chromaticity, and light intensity characteristics. For this reason, the light emitting devices are ranked and sorted (binned or graded) according to their light emission characteristics.
When multiple light emitting devices are used to manufacture illumination apparatus, it is desirable for all illumination apparatus to have uniform characteristics such as color temperature, chromaticity, and light flux. For example, lighting apparatus chromaticity range standards (refer to FIGS. 8 and 9) are specified by JIS (Japanese Industrial Standard) and ANSI (American National Standards Institute), and white-light obtained from an illumination apparatus may be required to be within a standard specified chromaticity range, or depending on the application, may be required to be within an even narrower chromaticity range. In particular, it is desirable for the light temperature to also be within a JIS specified light temperature along the black-body (radiator) locus (or Planck curve in color space).
However, standard light emitting device grade selection might be insufficient for producing illumination apparatus with this kind of minimal variation (dispersion) in illumination characteristics, and further (tighter) binning to obtain desired chromaticity or light flux results in increased manufacturing cost.
On the other hand, by combining light from light emitting devices that emit different colors, and specifically where those colors have a complementary relation, it is possible to produce light that appears (to the naked eye) as the targeted color. Consequently, various light emitting device mounting schemes have been proposed to produce an illumination device that emits light within a desired color range by assembling a plurality of component devices that individually emit different colors even outside the desired color range.
For example, with the purpose of making a pleasing white-light illumination apparatus for lighting applications, light emitting devices are used that have chromaticity located (in color space) outside the area of a 3-step MacAdam ellipse around a targeted color temperature, which lies on the black-body locus and is considered suitable for white-light illumination. A light emitting apparatus has been proposed (Japanese Laid-Open Patent Publication 2013-45544) that is characterized by a light emitting device module carrying a plurality of light emitting devices, which emit light that merges to emit with approximately the same chromaticity as the targeted chromaticity even though each of the plurality of light emitting devices has chromaticity lying outside the 3-step MacAdam ellipse at the targeted chromaticity.
In the manufacture of apparatus for light emitting device applications other than lighting, such as liquid crystal display backlighting, light emitting devices having the desired color temperature as well as light emitting devices having other color temperatures are used to produce an overall uniform color temperature. Manufacture results in different grades (color ranking) of the component light emitting devices and their maximum utilization is an (additional) issue. Accordingly, a method of manufacturing light emitting device application apparatus (Japanese Laid-Open Patent Publication 2008-147563) has been proposed with the following steps. A color temperature distribution data acquisition step gathers color temperature distribution data that include color temperature coordinates for light emitting devices manufactured at each designated production facility. An optimum color temperature grouping step identifies groups of light emitting devices, which emit merged light with a specified color temperature based on the acquired color temperature distribution data, and forms those groups in a manner that maximizes light emitting device utilization. An optimum color temperature sorting and mounting step sorts and mounts subgroups of light emitting devices identified as optimal for the light emitting device application apparatus such that the merged light of the subgroups has the prescribed color temperature.